AWS now comes with Redis, while Windows Azure promises faster response times

The competition between Microsoft's Windows Azure and AWS (Amazon Web Services) has moved to the caching layer: Both companies updated their caching services this week.

Caching services can improve response times for applications by delivering frequently consulted data and functionality from a server's working memory, or RAM, without calling it up from a slower hard drive.

AWS has expanded its ElastiCache service with a second popular open-source caching engine, Redis. The company has offered Memcached, on object storage cache, for some time.

Like Memcached, Redis offers an in-memory key-value store, one good for storing sorted sets and lists. ElastiCache supports Redis' master/slave replication capabilities, making it useful for offering multi-zone redundancy. AWS' Redis service currently is offered in beta form.

To help administrators get up to speed on this new technology, AWS will hold a Web seminar on how to use Redis on Sept. 26.

The service now features larger cache sizes and reduced latency. Unlike the old service, the new caching service will be run on its own servers (making it, in Microsoft's parlance, a "dedicated" service), instead of alongside the application itself, where it would use memory otherwise dedicated to the application.

The Windows Azure Cache Service can be used with any Windows Azure application -- including those running on Linux virtual machines. Eventually the company will configure the service to work with Windows Azure Mobile Services as well.

Users can allocate up to 150GB of in-memory data objects or content, and the memory can be dynamically increased or decreased without the need to restart the application it supports.

At present, the new version of Windows Azure Cache does not support Memcached, though Microsoft is planning to add support for Memcached in the future.

Neither AWS nor Microsoft has indicated when their updated services will graduate from preview mode to full commercial offerings.